1. Field of the Invention
The present invention relates to a diamond semiconductor expected to be developable as an electronic device manifesting various characteristics, such as high output, high stability in harsh environment, etc. and to a method for the fabrication thereof.
2. Description of the Prior Art
In recent years considerable attention has been focused on diamond, from the standpoint of its excellent physical properties, as a material for electronic devices capable of manifesting various characteristics such as high output, high speed, high frequency, low loss, high stability in harsh environment, etc. In order to realize the development as such electronic devices, it is necessary to establish a technology of controlling electrical conductivity (p-type or n-type) by addition of dopant elements. While various methods have been adopted for this conductivity-controlling technology, development of a conductivity-controlling technology according to the ion implantation method has been demanded in particular. There has been an increasing demand for the fabrication of diamond semiconductors according to the ion implantation method.
Various attempts have been made to fabricate diamond semiconductors using the ion implantation method. As dopant elements, various elements have been added. For example, an attempt has been made to fabricate a p-type diamond semiconductor by addition of boron.
Although it has been confirmed that a diamond semiconductor fabricated by addition of boron exhibits p-type conductivity, the diamond semiconductor cannot be put into practical use in terms of resistivity.
Another attempt has been made to fabricate an n-type diamond semiconductor by addition of phosphorus, lithium, etc. as dopant elements, using the ion implantation method. However, this attempt has not yet been succeeded in. Realization of this attempt is a subject matter in using diamond as the material for an electronic device.
The present invention has been accomplished in view of the above. An object of the present invention is to provide a diamond semiconductor controllable in conductivity by the ion implantation method and developable as an electronic device and a method for the fabrication thereof.
To attain the above object, the present invention provides a diamond semiconductor comprising a high-quality thin diamond film layer with few crystal defects and few impurities, implanted with ions of dopant elements and controllable in conductivity determined by a kind and a concentration of the dopant elements.
The high-quality thin diamond film layer with few crystal defects and few impurities includes a thin diamond film layer that can emit ultraviolet light at room temperature by excitation using electron beam irradiation when it has a thickness of not less than 200 nm.
The present invention further provides a method for the fabrication of a diamond semiconductor, comprising the step of implanting ions of dopant elements into a high-quality thin diamond film layer with few crystal defects and few impurities under conditions (implantation energy and implantation amount) that can attain given distribution of concentrations of the dopant elements and with the high-quality thin diamond film layer kept to a temperature in accordance with the conditions so as not to be graphitized, to thereby enable the diamond semiconductor to have conductivity determined by a kind and a concentration of the dopant elements.
The ion implantation conditions include implantation energy in the range of 10 keV to 1000 keV, an dopant element concentration in the range of 1xc3x971016 to 1xc3x971021/cm3. Furthermore, the thin diamond film layer is maintained at a temperature of room temperature to 800xc2x0 C. so as not to be graphitized at the ion implantation process.
When ions of an element serving as an n-type dopant are implanted into a high-quality thin diamond film layer, since the layer has few impurities and few crystal defects, electrons of the dopant element can be excited into a conduction band and move with ease. It is conceivable that this is why the diamond semiconductor of the present invention can have n-type conductivity. When ions of an element serving as a p-type dopant are implanted into a high-quality thin diamond film layer, since the layer has few impurities and few crystal defects, holes can excited into a valence band with ease and move freely. It is conceivable that this is why the diamond semiconductor of the present invention can have p-type conductivity.
The above and other objects, features and advantages of the present invention will become apparent from the description of the invention to be given herein below with reference to the accompanying drawings.